Hybrid vehicles utilize electrical storage batteries of large capacity to store energy recaptured during decelerations of the vehicle. In operation, the batteries are sources of heat. The heat must be rejected to the environment to preclude shortened operational life of the battery packs. Drawing the needed cooling air from within the cabin assures a narrower range of cooling air temperatures than would be the case using outside air. However, the use of cabin air also introduces fan noise through the path to the air inlet.